The use of cables to actuate or control devices attached to the end of the cable is very common. In a typical automobile, cables connected to control levers typically are used to open latches for hoods and trunks as well as to actuate the parking brake. In each of these uses, some form of lever is used to multiply either the force applied to the cable or the distance that the cable is pulled. Each end of the cable is securely fastened to either the actuating lever or the device to be actuated. Neither the control lever nor the actuated device move their respective locations.
A cable actuating system becomes more complicated when either the control lever or the device to be actuated must move, or travel, to adjust to the job being performed. Because of the complications, simple cable actuators are often replaced by motors that directly operate upon the device to be actuated. Motors and their related electronics add cost, however, and are often less durable than simple cable systems. For systems requiring intermittent but rapidly repetitive actuations occuring over the order of tens of milliseconds time, motor assemblies typically have speed limitations. Unless a motor runs idly, thereby wasting energy, motor start-up times typically exceed the required time limitations. Additionally, motors, gears, etc. add mass and occupy space to assemblies that must rapidly move as the device being actuated adjusts positions for different jobs.
In addition to motors, solenoids connected to levers or cables offer a common solution that enables rapid actuation with little extra cost or space. However, a typical low-cost solenoid requiring 1 amp at 36 volts has a throw length approximating only 8 mm. Where greater movement or travel is necessary, levers can be added to multiply the distance moved. However, the force applied by a solenoid is not evenly applied throughout the throw. Specifically, the force applied by a solenoid at the beginning of its throw is substantially less than the force applied as the throw nears completion. The result is that solenoid systems, while rapid, are disadvantaged by either limited throw lengths or unevenly applied force. Additionally, if a solenoid and lever must be added to an assembly that moves, then the extra weight must be accommodated by a larger motor that drives movement of the assembly.
Referring now to prior art FIG. 1, a combination of cables, solenoid, pulley, and lever is shown for a low-cost, repetitively rapid actuation system 10 not benefiting from the present invention. The system contains solenoid 11 with throw plunger 12 that moves in and out as the solenoid is activated. Throw plunger 12 is rotatably fastened to a short arm of lever 13 by dowel pin 19. Lever 13 is pivotally mounted about pin 14 such that downward movement of throw plunger 12 induces the long arm of lever 13 to move a considerably greater distance than the throw distance of throw plunger 12. Attached proximate to the end of the long arm of lever 13 is a cable engaging pulley 15 for engaging cable 16. When solenoid 11 pushes lever 13, then cable engaging pulley 15 pushes upward against cable 16, causing a “V” in the cable and pulling the two ends of the cable together by effectively shortening the cable's end-to-end length. Because of lever 13, the throw movement of cable engaging pulley 15 is much greater than the throw of solenoid throw plunger 12.
Among the shortcomings of the above system are that cable engaging pulley 15 must remain in contact with cable 16 in order to obtain full benefit from the upward thrust caused by lever 13. If the cable itself needs to slide due to repositioning of the device to which it is attached, then friction with engaging pulley 15 may cause rapid and excessive wear upon cable 16. Another shortcoming of the system shown in FIG. 1 is that the force applied as engaging pulley 15 begins to press upon cable 16 is less than the force near the end of its travel. This is a result of the varying force applied by solenoid throw plunger 12. Such weaker force at the beginning of a throw may be problematic in overcoming any friction or other resistance to actuating of the device attached to cable 16.
In applications requiring longer throws and intermittent but repetitively rapid actuations, a system better than the above is desired. One such requirement occurs in paper handling systems in finishers for printers and high speed duplicators. As sheets are fed into a paper tray, a tamper device is desired to tamp the sheets down in order to better position the paper and to minimize the paper stack height. One of the challenges for a paper tamper device is the need to adjust to different substrate sizes. The tamper device must be able to shift positions for various substrate sizes and shift from idle to rapid repetitive motion in a fraction of a second. The repetitive motion may be as fast as one down-and-up actuation every 150 milliseconds. An actuating device capable of such speed and repetition without excessive wear upon a cable and at acceptable weight, cost, and space requirement would be highly desirable.
One aspect of the invention is a cable shortening system for shortening the effective length of a cable having a section extended generally along one direction, comprising: a rotatably mounted bridged channel through which the cable is threaded in a rest orientation along one direction; and a mechanism, coupled to the bridged channel, for rotating the bridged channel; wherein rotation of the bridged channel to a second orientation shortens the effective cable length by deflecting a section of the cable away from the one direction.
A finishing system for finishing substrate sheets, comprising: (a) a substrate tray; (b) a tamper assembly for tamping substrate sheets located in the tray; (c) an actuating cable having a section disposed generally in one direction, said cable being connected to the tamper assembly wherein a pulling force from the cable actuates the tamping of substrate sheets; and (d) a cable shortening subsystem for shortening the effective length of the actuating cable, said subsystem comprising a rotatably mounted bridged channel through which the cable is threaded in a rest orientation generally along the one direction and a mechanism, coupled to the bridged channel, for rotating the bridged channel, wherein rotation of the bridged channel to a second orientation shortens the effective cable length by deflecting a section of the cable away from the one direction, thereby exerting a pulling force upon the tamper assembly.
Yet another aspect of the invention is a process for shortening the effective length of a cable having a section initially disposed along one direction, comprising: (a) rotatably mounting a bridged channel; (b) threading a cable through the bridged channel wherein the cable lies in a rest position along the one direction; (c) rotating the bridged channel to a second orientation wherein the effective length of the cable is shortened by deflecting a section of the cable away from the one direction.